1. Field of the Invention
The present invention relates to an image forming apparatus, more particularly to an image forming apparatus including a motor that drives the image forming apparatus, a controller that controls the motor, and a sensor.
2. Description of the Background Art
Examples of an electrophotographic image forming apparatus include an MFP (Multi Function Peripheral) including a scanner function, a facsimile function, a copying function, a printer function, a data communication function, and a server function, a facsimile machine, a copying machine, and a printer. Frequently the image forming apparatus includes a manipulation panel including a display unit and an input unit.
Many sensors are mounted on the image forming apparatus in order to detect a sheet conveyed in the image forming apparatus at each point, a position of a movable member, a state of an openable cover (door), or a size of the sheet disposed in a sheet cassette. Conventionally, in order to detect the states of the sensors, each sensor and a control board are connected by a wire.
Documents 1 to 6 disclose a technology of decreasing the number of wires in the image forming apparatus. Document 1 discloses a technology in which a pulse indicating the number of rotations of a servo motor measured by an encoder is converted into a position signal of an (high-frequency) alternating current, superimposed on a power-supply line, and extracted on a controller side. In Document 1, the number of rotations of the servo motor measured by the encoder is converted into the high-frequency AC signal.
Document 2 discloses a motor control device including a motor driver, a motor position detector, and a power cable through which an electric power is supplied from the motor driver to the motor position detector. The motor position detector encodes parallel information on the motor position into serial information, and transmits the encoded serial information to the motor driver through a coupling circuit using the power cable. The motor driver receives the serial information from the coupling circuit, decodes the serial information into the parallel information, and drives a motor based on the parallel information.
Document 3 discloses a technology of reducing an influence of a noise by conducting communication between edges of a PWM (Pulse Width Modulation) signal.
Document 4 discloses a technology in which an encoder that outputs A-phase, B-phase, and Z-phase pulse signals and a controller are connected through two signal lines to superimpose the Z-phase pulse signal on the A-phase and B-phase pulse signals.
Document 5 discloses a technology, in which A-phase, B-phase, and Z-phase encoder signals are transmitted while an amplitude modulation is performed to the A-phase, B-phase, and Z-phase encoder signals using U-phase, V-phase, and W-phase magnetic pole signals.
Document 6 discloses a technology of superimposing U-phase, V-phase, and W-phase magnetic-pole-position signals on a Z-phase origin signal in an encoder attached to a synchronous type AC motor in which a rotor is constructed by a permanent magnet.    Document 1: Japanese Patent Laying-Open No. 8-168283    Document 2: Japanese Patent Laying-Open No. 2003-18874 (U.S. Pat. No. 3,702,828)    Document 3: Japanese Patent Laying-Open No. 2005-62951    Document 4: Japanese Patent Laying-Open No. 5-260783    Document 5: Japanese Patent Laying-Open No. 5-207775    Document 6: Japanese Patent Laying-Open No. 4-331488
Because the many sensors are mounted on the conventional image forming apparatus, a wiring route becomes complicated between each sensor and the control board, and a space is required to ensure the wiring route in the image forming apparatus. A connector is required on a control board in order to connect each wire to the control board, which enlarges a size of the control board. In recent years, there has been an increasing demand for downsizing of the image forming apparatus. However, the space for the wiring and the connector on the control board prevent the downsizing of the image forming apparatus.
Additionally, numerous sensors and wires are required in a medium-size or large-size image forming apparatus that are particularly used in an office. Therefore, unfortunately, it takes a long time to assemble the image forming apparatus, and the connector is possibly connected to a wrong point to generate a connection failure of the connector. As a result, unfortunately, assembly work and maintenance work are inefficient, and an assembly cost and a maintenance cost (service cost) are increased.
In the technologies disclosed in Patent Documents 1 to 3, in which the motor signal is superimposed on the power-supply line while modulated, a circuit that processes the analog high-frequency signal is required on not only the motor side but also the control board side. Therefore, a structure is complicated and high cost. Because an interface for the motor signal is specially configured, a degree of freedom of motor selection is significantly decreased. The motor used in the technologies disclosed in Patent Documents 1 to 3 is frequently incompatible with a small-size image forming apparatus in which a mechanism reducing a wiring amount is not required because of the relatively small wiring amount, and therefore the motor cannot be applied in the small-size image forming apparatus. The above problem cannot be solved by the technologies disclosed in Patent Documents 4 to 6.